1. Field of the Invention
This invention relates to a method and apparatus for cutting laminated articles made from glassy metal alloy. More particularly, the invention relates to a method and apparatus for cutting magnetic cores spirally wound from ribbons of glassy metal alloys which will not delaminate or deform such cores.
2. Description of the Prior Art
It is well known that magnetic cores around which coils of wire can be wound are used in many electrical components such as inductors, transformers and the like. The cores often define substantially closed loop magnetic circuits, such as toroids, but in some applications, air gaps are introduced in the magnetic core circuits to increase the magnetic reluctance of the circuit and to produce certain desirable magnetic characteristics. Such cores, generally referred to as cut cores, are used in devices such as transformers, inductors and motor starters. The applications often employ "C" type cut cores wherein an oval or rectangular shaped, closed loop core is cut to create matching C-shaped cores. Such cut cores have a high reluctance air gap which can be adjusted by inserting suitable spacers between the matching surfaces of the mated C-cores to tailor the magnetic circuit characteristics to the particular application. To obtain the desired magnetic circuit characteristics, it is important that the mating ends of the cut cores are well matched; as close as possible to 100 percent of the surface areas of the mated ends of the cut cores should be in contact. If the ends are mismatched, the power loss in the core and the VA (volt-ampere) characteristic of the core are adversely affected.
Present cores are ordinarily wound from tapes or ribbons of crystalline metals, such as iron nickel (FeNi) and iron silicon (FeSi) alloys, wherein the wound construction, providing successive multiple layers of material, has the advantage of reducing core power losses caused by eddy currents. Since the crystalline metal alloys are ductile and have low yield stresses, the tapes are easily wound into the desired shapes. Once wound and annealed, the tape material takes a permanent "set" and contains little residual stress. Conventional binding methods such as resin impregnation of the laminations, core edge coatings and plastic cladding of the wound core are then sufficient to hold the laminations in place during subsequent manufacturing operations. The cores can be cut with conventional cutting means, such as blades and cutting wheels, without special handling procedures, and when cut, the cores retain their shape. The cut ends, after grinding and polishing will match well and have little tendency to bow outwardly creating mismatched C-cores.
Because of the favorable magnetic properties of glassy metal alloys, such as high magnetic permeability, low core loss and low VA characteristics, they are especially useful as magnetic core material. Glassy metal alloys, however, are thinner, tougher, harder and more elastic than the crystalline metal alloys ordinarily used in magnetic cores. As a result, they are less easily wound into the desired core shapes and are less likely to maintain the shapes after the wound cores are cut. In addition, glassy metal tapes and ribbons have some variations in thickness because of the way those materials are manufactured. Consequently, winding glassy metal ribbons to produce a closed loop core shape induces significant internal residual stresses which cannot be completely relieved by annealing the wound cores. Resin impregnation of the core laminations, core edge coatings and plastic claddings can add rigidity and help hold the core laminations together, but even when these preparatory procedures are used, glassy metal cores cannot be satisfactorily cut using ordinary cutting procedures. The layers still tend to delaminate, and the cut ends tend to deform and twist out of position creating mismatched core ends. As a result, the apparatus and procedures ordinarily used to cut magnetic cores wound from glassy metal ribbons produce delaminated and deformed cores having degraded electromagnetic characteristics.